# Update to Turboprop section in Sustainable Energy - without the hot air

On page 35 of SEWTHA I wrote this:
Q: Aren't turboprop aircraft far more energy-efficient?
A: No. The ``comfortably greener'' Bombardier Q400 NextGen, ``the most technologically advanced turboprop in the world,'' according to its manufacturers [www.q400.com], uses 3.81 litres per 100 passenger-km (at a cruise speed of 667 km/h), which is an energy cost of 38 kWh per 100 p-km. The full 747 has an energy cost of 42 kWh per 100 p-km. So both planes are twice as fuel-efficient as a single-occupancy car.
 ATR600 - all images from atraircraft.com
but I'd like to now make this addition:
It is claimed that the even-greener ATR72-600 is about one third more energy efficient than the Q400, using 25 kWh per 100 p-km (2.5 litres per 100 passenger-km, at a cruise speed of 560 km/h).
And thus I should perhaps update my answer to this question from "No" to "Maybe -- the best turboprops are a little more energy-efficient".

Thanks to Matthieu Beaumel for pointing me to this!
Incidentally, while I'm writing, I'd like to nominate the advertisers of the ATR 72 for this year's Hot Air Oscar for the most misleading "green" infographic, for this astonishing picture [at left] showing the difference between the fuel consumption of the ATR 72 and the Q400 on a 250-nautical-mile journey. As the numbers in the picture show, the ATR 72's fuel consumption is 70% of the Q400's, but the volume of the three-dimensional blue barrel shown is 30% of the volume of the orange barrel — a 2.3-fold exaggeration!
 blue barrel : orange barrel ratio of diameters 91 : 134 =0.68:1 ratio of heights 118 : 179 =0.66:1 ratio of volumes (as depicted) =0.68×0.68×0.66 =0.30:1 true ratio of volumes(735:1043) =0.70:1
But hey, in mitigation, they are contributing to a sustainable air transport development, so exaggeration is ok!

David MacKay